The pioneering Stuxnet computer virus, which was designed to attack a single Iranian uranium enrichment facility, went on to infect PCs around the world. Security experts have identified thousands of resulting Stuxnet infections. On Monday, multinational energy giant Chevron became the first U.S. company to admit that it, too, was infected by Stuxnet.

Chevron found that some of its systems had been infected by Stuxnet soon after security firms discovered the virus in July 2010. "I don't think the U.S. government even realized how far it had spread," Mark Koelmel, general manager of the earth sciences department at Chevron, toldThe Wall Street Journal. "I think the downside of what they did is going to be far worse than what they actually accomplished," he said.

But according to Chevron spokesman Morgan Crinklaw, Stuxnet caused no damage to Chevron's network. "We make every effort to protect our data systems from those types of threats," he told The Wall Street Journal.

Confirmation that Stuxnet was designed by the U.S. government -- reportedly working with Israel -- came in June 2012 via journalist David Sanger, who reported that Stuxnet was developed as part of a classified cyberweapons program codenamed "Olympic Games," which was begun under President Bush and accelerated by President Obama. The malware was designed to forestall Israeli airstrikes against Iran, instead using a virus that sabotaged the high-frequency convertor drives used in centrifuges inside the Iranian nuclear facility at Natanz.

Stuxnet reportedly did disable a number of centrifuges at Natanz, but it also spread. "The fundamental problem with the use of viruses as weapons is that once deployed, one loses control of it. It is as likely to damage one's friends as one's enemies," said William Hugh Murray, an executive consultant and trainer in information assurance who's an associate professor at the Naval Postgraduate School, in a recent SANS Institute newsletter.

People with knowledge of the Olympic Games program, speaking to Sanger, did say that the virus had unexpectedly gotten out of control. But many security experts have disputed the notion that Stuxnet somehow broke loose unexpectedly, given that it was a virus incorporating multiple infection techniques, including the ability to exploit four zero-day vulnerabilities.

"'Escaped' continues to be a puzzling term when applied to a virus that relied on numerous Microsoft zero-day vulnerabilities and propagation vectors," said Sean McBride, the director of analysis for Critical Intelligence, in a SANS newsletter. "On the other hand, if your system was not the single underground facility in Iran that Stuxnet was intended to disrupt, the infection was benign. Such collateral damage is part of the price industry gets to pay for -- what was then -- two more years of Iran [being] without a nuclear weapon."

What remains worrying about Stuxnet is the ease with which the custom malware was able to surreptitiously alter the behavior of programmable logic controllers (PLCs) used in industrial control systems. As the Chevron infection highlights, PLCs aren't just used in uranium refineries, but for a broad range of applications -- spanning oil and gas enrichment, manufacturing plant floors and even prisons. Furthermore, businesses might replace their industrial control systems only every 10 or 20 years.

In the interim, what could safeguard PLC environments against future attacks of the Stuxnet variety, especially if launched by foreign adversaries? "There are no automated defense systems that can protect power systems and other critical infrastructure resources against these advanced attacks," said Alan Paller, director of research at the SANS Institute, in a SANS newsletter. "The only defense -- admittedly imperfect -- is radically improved technical skills."

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